During 1989 and 1990 Unocal developed the capabilty to apply true 3D pre-stack depth migration to 3D seismic reflection data. The technique was applied to a 3D data set from the Gulf of Suez, Egypt, over a sub-salt prospect initially identified from 3D post-stack time migrated data. The prospect was subsequently drilled by Unocal Egypt as operator for a group including LASMO Oil (Egypt) Ltd and Nedlloyd Energy (Suez) BV. The paper describes, in the form of a case history, the processing and interpretation of the data and the drilling results proving the effectiveness of the technique.